The present invention relates generally to manually shifted transaxles of the type used in combination with small air cooled engines in vehicles such as garden tractors and ride-on mowers, and more particularly to such a transaxle having an in-line-shift speed change transmission.
Manually shifted transaxles of the type concerned herein often employ a main shaft carrying a plurality of freely journalled speed change gears which can be selectively coupled to the main shaft by a shift mechanism. Each of the speed change gears is in constant running mesh with one of a plurality of companion gears affixed to a counter shaft which rotate together in unison. Power input to the transaxle is via a bevel pinion gear engaged with a bevel gear affixed to the counter shaft. Power output from the main shaft to the output drive shafts is via a differential. One such transaxle arrangement is shown in U.S. Pat. No. 4,673,055.
One variation of the above-described configuration is shown in U.S. Pat. No. 4,662,241, in which the bevel gear is freely journalled on the main shaft and has a spur gear integrally formed with the bevel gear. The integral spur gear is in constant running mesh with one of the companion gears so that power can be transmitted from the bevel gear to the counter shaft. Speed selection is accomplished by an axially shiftable spring shift key on the main shaft which selectively engages radial keyways in the speed change gears to couple the selected gear to the main shaft. One of the gear pairs on the main shaft and the counter shaft can be eliminated by providing radial keyways in the bevel gear so that the bevel gear can be coupled directly to the main shaft without transmitting power through the counter shaft.
As illustrated in U.S. Pat. No. 4,662,241, the main shaft on which the bevel gear and speed change gears are journalled is of a relatively large diameter. This allows the shift keys to engage the keyways of the gears at a radial distance sufficiently removed from the axis of the main shaft to avoid excessive shear forces on the shift keys and keyways. However, this relatively large diameter sets a lower limit to the diameter of the speed change gears which are journalled on the main shaft, thereby limiting the overall speed change ratio which can be accomplished with the transmission. The present invention overcomes the aforementioned limitation and permits a wider range of ratios in the transaxle.
It is relatively common to employ a chain drive between the reverse gear on the main shaft and its corresponding gear on the counter shaft to effect reversal of drive direction. The use of such chains make it relatively more difficult to assemble the transaxle than if the transmission gearing were strictly composed of spur gears. Chain drives also generate more noise and are subject to greater wear. An alternative is to employ a third spur gear between the reverse gear and its companion gear on the counter shaft which is in constant running mesh with both gears. This, however, requires a third stub shaft to support only the intermediate reversing gear. The stub shaft requires some sort of bearing support in the transaxle housing which generally would not be in the same plane as the main and counter shafts. Consequently, the technique of providing a transaxle housing split along the plane in which the main and counter shafts lie in order to simplify assembly of the intermeshed gears into the housing would not appear to be available to simplify the mounting of the intermediate reverse gear stub shaft. A further assembly step of mounting the stub shaft in its own bearing would appear to be necessary. The present invention overcomes the apparent difficulty discussed above.